MikeMc

Being an old time 2c guy and getting a lot of help in another thread about 4c engines this makes me think of some other questions, but here's what I've learned...

- .56 4c makes a good replacement for a .40 2c
- .56 4c is great but still doesn't make as much HP as a .40 2c
- .70 4c is recomended if you really need the same power as the .40 2c

So do we really need all that power? Personally I hardly ever go vertical and fly 95% of the time between 1/3 and 2/3 throttle. On sport planes or aerobatic planes (not full on pattern or 3D) what manuvers require all the .70 4c power? What I'm trying to decide is if I really need to replace all the .40 2c power with identical 4c power (.70 4c) or if I can go with less (.56 4c). 2 plane example: Tower Fun-51 - flying now, Midwest Sukhio - building. Basic to lower-mid level aerobatics. Rolls, loops, knife edge, hammer head, flat turns (don't know if there's a better name for flat turn). Nothing serious. Let me know your opinion.

thanks,
Mike

Fastsky

If the winds are light, the grass is short, and its not too hot out then a 56 4 c will fly the plane just fine. Now say its been raining and the grass(runway) hasn't been cut in 2 weeks. Its going to take a bit more oomph to pull the plane through the grass up to takeoff speed. Either that or use up the whole runway and hope its up to speed! Another scenario that happens here a lot. You take off and fly around for say 3 minutes. Then suddenly the afternoon winds whip up and now your fighting 15-25 km gusts! The larger prop that the 72 4c can turn now might be the only reason that you can make it back to the runway and land in 1 piece. With out the extra power you can end up watching your plane get tossed backwards making large loops until its out of sight or it crashes. From my experience; going too big creates its own problems. Going a bit bigger is usually an advantage. Especially if the larger engine fits the same size motor mount. I have been running 75 2c engines on 60 size planes with great results.[8D

MustangFan

When you rip the firewall off the plane at three clicks above idle ... backoff a little.

I read quite a few post on RCU where they are definitely over-powering their plane. [X(]

You seem to have a good idea of what it takes.

One thing I like is being able to throttle back when flying straight and level, so I go for the max suggested engine for the plane.

I like the sound of the engine better at partial throttle ... seems to sound more realistic.
Especially four cycle planes.

taurus02914

Too much power ha ha ha ha ha ha ha
to much power isnever enough!
Always Fly Fast And Low

Fastsky

I have found 1 disadvantage. Going too big on planes that like to float on landing makes it hard to get them to come down![8D]

MinnFlyer

My Feedback: (4)

I recently reviewed a plane called a Dragon 40 (review not posted yet) in which I used an OS 52 4-stroke. This combination was perfect. The Dragon is a very light plane with an airfoil similar to a Cub (See pic).

On something like my Goldberg Cub, I prefer an OS 70, because the Cub is a bit heavier, and I like to wring it out a bit. Plus, I add floats to it and fly it off of the water. The extra power is really needed there.

If I were going to put it into anything that would be considered aerobatic (Extra, Edge, Cap, etc.) I would definately go with a 70 size 4-stroke.

trroscoe

My Feedback: (39)

I had a GP 40 size ultimate that started life with a 46FX on it. This engine flew this plane around good and it would even do some mild 3D stuff. I replaced it with a Saito 72 that I happened to get my hands on and WOW what a difference this made in the way the plane would fly. The saito weighed about the same as the FX so I didn't even have to move any thing to get the balance right. This engine made the plane really come alive. It had unlimited vertical and was so much fun to fly because it had power to spare. It flew at about the same speed but any vertical manuver was much better. It also sounded cool. I finally moved on to larger planes so I sold it. I have 4 strokes on all of my small planes and love them. My flying buddy has a GP super sportster 40 and he has a saito 56 on it and it pulls that plane around with authority. I would personally go with the larger engine as most of the time they weigh the same and are usually not much more money.

rick

DBCherry

My Feedback: (4)

I'm going to contradict what pretty much everyone else (including you MikeMc) has said.

I flew my trainer (a PT 40) with an OS 40 FP, pretty much equal to today's 40LA, and it flew fine. My second plane was a Great Planes Super Sportster. I also put a 40 FP on that, and it flew fine too.

I am currently (8 years later) flying a new Super Sportster and I have a Thunder Tiger 54 four stroke on it. It's performance is at least equal to the performance I had with the FP, and I believe it's a bit better.

I do NOT think that a 70 four stroke is equal to a 40 two stroke, it is at least half again as powerful. I DO believe that a 54 (56) four stroke is equal to a 40 two stroke.

Mike Mc,
From your last paragraph I believe that you'd find the 56 four stroke to be plenty of power for your type of flying. Buy one for the Fun 51 and I don't think you'll be disappointed.

By the way, my Sportster will do large, round loops with the 54 four stroke, and it will do outside loops just fine as well. No, it won't climb vertically more than about 50 to 60 feet from a level run, but I don't do 3D so....

But as Minnflyer said, if I were flying a float plane I'd go with a 70.
Dennis-

zetor

My Feedback: (2)

I really like my SS 40 Dennis. I put 6 flights on it and more power is the last thing I need. It has a .46. I read a thread on the sportster where people were putting .61 engines in them. That seems like that would be overpowered to me. I'm always a little nervous about thing starting to break off.

phread59

Tower 51 I would use a 56. The Sukhoi I would use the 70. The Sukhoi has more drag in the airframe (unless it is a profile, I am unfamiliarwith this plane. Your decision must be tempered by 2 factors. 1- what am I going to do with the plane. Am I going to 3D or just putt around. Do I want to fly fast ect.

2- what type of airframe it is going on. A profile does not have a lot of drag. A Super sportster is a very slippery design. A bipe has a lot of drag. A Cub has a lot of wing and so on-and so on.

I would sit down and plot out what planes I wanted and how I wanted to fly them. Then buy the appropriate engine. And always look to the future as well. Don't buy an engine that after the model it is on will be useless to you. The last thing I do is I do not go outside the manufactuer's reccomended sizes. I hope this helps.

Mark Shuman

MinnFlyer

My Feedback: (4)

Yes, but Dennis, you're comparing a 40FP to a 54 4-stroke. How would that 54 compare to a 46FX?

In fact, that's probably a pretty good comparison,

40 bushing = 50-ish 4-stroke

46 Ball Bearing = 70-ish 4-stroke

taurus02914

I do not beleive the comparisons between 2 and 4 strokes are made all that easy, to say a .40 2stroke is compared to a whatever 4 stroke would not be all that accurate there are all different types of 2 stroke engines. The .40 fp or the .40 la are probubly the least powerful .40 size engines going, oh i forgot to mention the tower stuff... if you step up to a higher performance 2 stroke engine the same comparison doesnt apply.
I think the comparison should be made between individual engines to be more accurate.
Just a thought .
Most knowledge in R/C is only a matter of oppinion.
But mine is always right he he he

DBCherry

My Feedback: (4)

Mike,
I compared a 56 to a 40 because that was what he asked about.No, I do not think a 56 is comparable to a 46 like the OS FX, or even the TT 46 Pro. But I think a 70 four stroke produces a bit more pulling power than one of those 46's.

And you're right taurus, it is all opinions, but it's mine that are right.
Dennis-

smokingcrater

I've flown both my irvine .53 and saito .72 4 stroke in the same plane. the saito DOES have more power, but not by much. I have no doubts the saito .72 is more powerful then any general purpose .46.